Process of making chromates



March 24, 1925.

Filed Dec. '7, 1922 5 Sheets-Sheet l Q m m w op b .a 4,. R E uw m N M mw ...MN JN MG l. .1 [mi \*N l o n NN \N v/ \N .WNW N 4 Mam-4, 1925 1,531,088

, G. P. FULLER Y PROCESS OF MAKING `CHROMATES Filed Dec. '7, 1922 3 Sheets-Sheet 2 March 24, 1925'.

1,531,088 G. P. FULLER PROCESS 0F MAKING CHROMATES Filec Dec. '7, 1922 4 5-SheetsSheet 5 Snom/4:05

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.Panarea Mu. 24, 1925.

UNITED STATES PATENT oFFlcE.

emEcE P. FULLER, or LA SALLE, NEW Yonx, AssIGNon, EE MEsNE ASSIGNMENTS,

- To EDWARD nIcHAEL, or BUEEALdVNEw Yonx.

raocEss or MAKING cHa'omArEs.

Application led December 7, 1922. Serial No. 605,360."

To all 'whom itmay concern:

Beit known that I, GEORGE P. FULLER, a citizen of the United States, residing at La Salle, county of Niagara, and State of vNew York, have invented certain new and useful Improvements in Processesl of Making Chromates, fully described and represente in the followin speciication and the accompanying drawings, forming a part of the same. Thisl invention relates to an 'improved process of makingchromates.

In the prior processes of making chromates, it is customary to roast a chrome ore with an alkali met-al carbonate and an inl fusible alkaline absorbent material or carrier such as lime, in an oxidizing atmosphere. The chrome ore heretofore employed and' known as chromite,- comprises the. chrome compound represented by the formula l3`eO.Cr. ,O3 and some gangue. This ore in a comminuted condition is mixed with an alkali metal carbonate, for example, either tassium or sodium carbonate, and lime.

. he mix is then roasted in an oxidizing atmosphere at Aa temperature of about 1000o to 1100'C. The chrome compound FeO.-

` This mass of ythe CrO3 reacts with the potassium or sodium carbonate. If, for example, sodium carbonate be used in the process, .as is common,

the CrO,s reacts with .the NaCO3 to formY Na,CrO,. Because sodium carbonate fuses at a temperature around 849 C. and sodium chromate at a lower temperature, the lime acts as an infusible alkaline absorbent material to hold the fused sodium chromate and the fused sodium carbonate so that they will not flow out of the furnace. At the completion of the process as heretofore carried out, the reaction has not usually been complete, sothat the final product has been a `mixture of sodium chromate, lime, and gangue with some unconverted FeOCr2O3 and some sodium carbonate, the latterand the sodium chromate being in a fused condition.

asty material when discharged from t e furnace in the manner customa in the prior proce quickly cools in large locks or cakes. These blocks are then leached in batches in a. leaching tank, the sodium chromate and the sodium carbonate, if any, going into solution. This solution is then drawn of for further treatment to recover the sodium chromate.

The largemasses or blocks ofthe solidiied materlal are difficult to leach and processes have been suggested where the said masses are first crushed and then go to the leaching vats. These processes, however, have been objectionable on account of the considerable amount of dust produced and partly lost during the crushing and handling of the material. Furthermore, the crushing process involves an additional expense.

The purpose of the present invention is to reduce the labor involved in the prior processes and to improve the efliciency.

The invention will first be described in connection with the accompanying drawings and then more particularly pointed out.

In the drawings:

Fig. 1 is a broken plan view, partly in section, of an apparatus particularly suitable for carrying out the invention;

Fig. 2 a broken longitudinal section on the line 2-2 of Fig. 1;

Fig. 3 a front e'nd view, partly in section,

Vlooking in the direction of the arrow 3,

Fig. 2;

ig. 4 a rear end view, partly in section, lhooki'ng in the direction of the arrow 4,

Fig. 5 a transverse section on the line 5--5,

ig. 6 a side elevationeof the cable operation mechanism, showing also a side view near the front `end of the furnace with the agitating or rabbling mechanism withdrawn from the furnace;

Fig. 7 a detail plan view of the cable drum and its operating mechanism; and Figs. 8, 9, and 10, detail views of the plows or Scrapers.

In carrying out the new process the same mixture is used as in the old process. This mix comprising comminuted chromite ore,

accompanied usually by some gangue, an alkali carbonate, preferably sodium carbonate andan absorbent material such as lime, aO, is roasted at a temperature of' about 1000 Cain an oxidizing atmosphere and is Well agitated so as to insure good contact of the material with the atmosphere. Then, while stillmaintaining the agitation and the oxidizing atmosphere the material is cooled gradually until it reaches a temperature at or below its point of solidification. As a result Lof this process the material is maintained in a granular condition and is discharged from the furnace as a mass of separate, solid, and nonadhesive granules, which will no longer adhere to one another.

The agitation to bring about the granular condition o-f the final product mustbegin in the furnace when the material is pasty or adhesive and must continue until the granules have cooled to a nonadhesive condition, before discontinuing the agitation. During this cooling and agitating step of the process the oxidizing atmosphere is maintained because in practice it is found that thereby any F eO.Cr,O3 which escapes conversion at the hottest part of the furnace can still be oxidized and converted into sodium chrof mate during the cooling state. Hence not only is a better product obtained but the eiiiciency of the process is enhanced.

`In the best example of the process, the starting materials are ground to a fine powder. The lime and the sodiumcarbonate are ground so that none will be coarser than 100 mesh. The ore is ground fto pass 130 mesh. The ingredients, after grindin ,are very thoroughly mixed, special effort being made to produce a uniform mixture. While the proportions may be varied according to the' nature of the ore -and the quality of the materials, the following proportions by weight have been found satisfactory, viz,

vParts. Chromite 415 Lime 415 Sodium. carbonate 270 The sodium carbonate may be employed in the form of soda ash, in which case the amount of soda ash is taken so as to give the proportion of sodium carbonate as stated above.

This mixture of comminuited materials is then fed to a furnace which has a hot zone whose temperature is sufficient to heat the mix to about 1000 to 11000 C. In the hot zone anl oxidizing atmosphere is maintained, as, for example, by providing `a free flow of air through the furnace over the mix. The

latter is well agitated in order to insure a good contact between the air and the particles of the mix. The furnace is so extended beyond the hot zone that a zone of gradually lowering temperatures is provided, which may be termed a cooling zone. From the hot zone the mix is fed to and through the sor-called cooling zone and during its travel through this zone is agitated and exposed to the oxidizing atmosphere in such a way that the pasty material in and coming from the hot zone is not allowed to cohere but is maintained as a mass of separate granules. This exposes more surface to the oxidizing atmosphere and hence causes a continuation lar condition is maintained until finally the material reaches a temperature below the fusing point of any materials it contains and is no longer pasty or adhesive. Therev upon the material is discharged from the furnace in a granular non-adhesive condition, and hence remains granular. In practice the material is allowed to,l cool to about 700 C. in the furnace and then is discharged therefrom.

The apparatus shown in the accompanying drawings is particularly suited for carrying out the new process on a large scale.

Referring to the drawings, A is a furnace having side walls 1, a top 2 preferably arched, as shown in Figs. 4 and 5, and a bottom divided into two hearths, 3 by a fver'tical slot 4 opening into a conduit 5 which extends the full length of the furnace and is open at each end.

The furnace chamber is provided with an outlet for the escape of gases. In the particular construction shown inthe drawings, the top or arch of the furnace is provided with a series of lues, as indicated at 6, communicating with a main iue 7 leading to a stack 8.

The bottom of the furnace extends outside somewhat beyond the top or arch at the front end so as to form charging tables, one at each side of the slot, as indicated at 9, Fig. 1. The mix ma be suitably supplied to these charging' tab es, but in the embodiment of the invention shown, suitable automatic means for supplying the mix` to the hearths is provided. In the present example this charging means comprises screw conveyors arranged 'n casingsl or trunks arranged below the heanths and arranged to force thevmix upward through openings 9 Vin the hearths thereby forming piles of t-he mix above the level of the hearth.

In the example illustrated each charging table has a plurality of openings, for example, two, and these are supplied with mix by the corresponding screw-conveyors as indicated at 10ia and 10". Each conveyor carries the mix from a boot, as indicated at 11, and each boot is supplied with mix from a hopper 12, by a rotary gate device 13, which carries measured charges of mix from the hopper to the conveyor boot. spective conveyors are driven in any suitable way.- .In the drawings, the shafts of the two conveyors at one side of the furnace: are provided with gear wheels 14, which mesh with an idler gear wheel 15. See Fig. 6. One of the conveyor shafts is provided with a pulley 16, driven from a suitable source of power, not shown.

The furnace is heated alongia part only The rellS of its length, thus forming a zone of maximum temperature. In the best embodiment of the invention such as that shown in the drawing, the zone of maximum .temperature is located at a portion of the furnace interthe furnace at the front end of the furnace' and what may be termed a cooling chamber at the rear end of the furnace. In the preheating section of the furnace the temperature gradually increases from the front to the hottest zone, while in the cooling chamber the temperature gradually decreases from the hottest zone toward the discharge end.

f Suitable means is provided for feeding the mix from the charging tables along the hearths of the furnace and for agitating the material In the example shown the means for feeding and for agitating comprises one unitary `structure performing both functions. This structure, as shown in the drawing, consists of a truck or trolley running on" tracks 18 in the conduit and carrying a standard 19 which is made narrow so that it may extend upward through the slot in the furnace bottom. This standard maybe made of two vertical plates,

suitably connected by end pieces, as shown.

The top of the standard 19 is above the hearths of the furnace and to it are secured girders as indicated at 20, which extend transversely substantially the full width of the furnace. The 'rders 2O may be suitably connected by cams 21 these girders and beams forming a frame as shown in plan in Fig. 1. In this frame four shafts 22 are journaled, one pair of shafts being at the front of the framework and the other pair at therear of the Yframe work. The shafts of each pair are in line with each other, and their adjacent ends are provided with cranks, indicated at 23. The cranks on the front air of shafts extend upward while the cra ks on the rear pair of shafts extend downward. The crank on the right hand front shaft is connected to the crank on the right hand rear shaft by a connecting rod 24 and the cranks on the left hand front and rear shafts are 'connected by another connecting rod 24. These two parallel connecting rods are both pivoted to an operat# ing lever 25 whose lower end is pivotally connected to an Yendless cable 26 which passes entirely through the conduit, around sheaves 27 and around va cable ydrum 28 arranged at one sideof the furnace, as shown in" Fig. It is obvious that if the cable is pulled in one directionit will first swing the operating lever 25 and thereby give a partial rotation to the four shafts 22. The amount of movement of the lever determines the extent of rotation of the shafts.k This movement of the lever is limited by stops 29 and 30 arranged one at each side of the lever, as shown in Fig. 6. When the cable pulls the lever 25 in a given direction, the lever comes into contact with the corresponding stop, after which the further travel of the lever moves the truck with its attached mechanism through the furnace.

On each shaft is mounted a series of radial arms. each provided with a scraper or plow blade 31. The blades are set on the shafts at an angle to the direction of travel of the structure through the furnace, being so arranged that when the bottom edges of ,the blades are parallel to the surfaces of the as left hand plows, as will be clear from Fig. 1. The arrangement of the rear plows is such that the plows nearest the slot in the furnace bottom tend to plow the material away `from the slot and toward the side walls while the plows nearest the side walls tend to plow the material toward the slot.

When the cable reverses its direction, that is, starts to move in a backward direction through the furnace it first swings the lever 25 to rotate the shafts to a limited extent and then pulls the truck and its attached mechanism backward. The rotation of the Shafts swings the radial arms upward away from the hearths, butv this brings the lower or trailing corner of each forward' plow into such a position that it drags in the peak of the furrow laid over by the rear blade when the mechanism was moving in the opposite direction. Therefore, the backward movement of the plows tends to form a small furrow in the top of each large pile, heap or window, thereby exposing more surface to the oxidizing atmosphere. In this way the material is pushed forward to a certain extent at each forward movement of the plows, and there is no backward travel of the material4 during the backward movement, but only a slight disturbance of a part of the material. This disturbance, however, is very important as it increases the surface area exposed to the oxidizing atmosphere and also brings fresh surfaces into contact with the air.

The cable drum 28 may be operated in any suitable manner to pull the cable in opposite directions to the desired predetermined extent. to employ an automatic apparatus which controls the operation of the cable drum. This automatic apparatus includes means for determining the interval of rest between operations of the drum in first one direction and then in the other, and also includes means for determining the extent to which the drum is rotated in each direction. In the specific' example illustrated in the drawings, the cable-drum 28 is fixed on a drum shaft 32 having its ends journaled in bearings 33 and 34 near the center of the shaft. A worin-wheel 35 is secured to it. This worm-wheel is engaged by a worm 36 fixed on aI driving shaft 37 which is journaled at its ends in bearings 38 and 39.

On the driving. shaft 37 are loosely mounted two pulleys 40 and 41 which are continuously rotated in opposite directions by belts such as a straight and a cross-belt driven from a suitable countershaft or the like, not shown.

Each pulley is provided with a clutchjaw, 40', 41', arranged to be engaged by corresponding jaws on the ends of a clutch sleeve 42 which is splined to the driving shaft, and is longitudinally movable thereon so as to be brought into engagement with either of the jaws carried by the pulleys. The clutch-sleeve has a grooved collar 43 secured to it, the groove in which is engaged by rollers 44 carried by the forked end of a CTI clutch-shifting lever 45 fulcrumed at -its upper end on a suitable frame work 46. ln the upper part of this framework is journaled a shaft 47 on which is iixed a large wheel 48. Two tanks 49 and 50 are mounted so as to move in unison with the large wheel 48, these tanks being connected at their bottoms by a pipe 51 having a suitable valve 52 capable of line adjustment, as, for example, a needle-valve. To the shaft47 is fixed an arm, 53, which is connected to the clutch-shifting lever 45 by a link 54.

The drum-shaft 32 has one end provided with a screw thread, as indicated at 32a in Fig. 7, and at each end of the screw threaded portion the shaft is provided with collars 55 and 56 adjustably fixed to the shaft. Mounted 4on the screw-threaded portion 32a is a nut 57 whose periphery carries or serves as a sprocket wheel 58, which engages a sprocket chain 59 whose ends are fixed to the large wheel 48 at opposite ends of a diameter of the large wheel. It is advantageous to provide the nut 57 on its opposite faces with axially projecting pins or lugs, one at each send, as indicated at 60 and 61. These pins or lugs are arranged to engage corresponding pins or lugs projecting axially from the collars 55 and 56, as indicated at 62 and 63.

In Fig. 6 the left hand tank 49 is shown as containing a liquid. This is usually a liquid hydrocarbon, and in practice keroeene is preferred. In the condition of the apparatus shown in Figs 6 and 7, the clutch sleeve 42 is connected 'to the right hand pulley 41 which is supposed to be rotating in the direction of the arrow. This will rotate the drum shaft 32 in such a direction as to cause the nut 57y which is held stationary by the sprocket chain, to travel towards the drum. As soon as the nut has traveled so close to the collar 56 that the lugs 61 and 63 are engaged, the nut 57 and its sprocket .wheel 58 will be rotated by the drum shaft and the sprocket chain will turn the large wheel 48 in such a direction as to elevate the left hand tank 49 and also to shift the clutch sleeve 42 out of engagement with the pulley 41 and into an intermediate non-engag-ing position. This stops the drum. Pipe 51 provides for air displacement.

The liquid in the elevated tank now flows through the pipe`51 into the lower tank 50, the rate of iow being determined by the setting of the valve 52. Then suiiicient liquid has flowed into the tank 50, so that its weight will overcome the friction of the appara-tus, this weight will cause the large wheel 48 to make a partial movementlof rotation in suchfa direction as to still further lower the tank 50. This motion causes the nut 57 to be rotated in such a direction that it will travel along the screw-threaded lug 61 from the lug 63.

to engagement with the pulley 40, and rel verses the direction of rotation of the drunishaft, at the same time causing the nut 57 to travel toward the outer end of the drumshaft, where it finally engages its lug 60 with the lug 62 on the collar 55. Thereupon the nut 57 and its sprocket-wheel 58 are rotated by collar 55 on the drum-shaft 32 and, through the sprocket chain 59, this motion is transmitted to the large wheel. 48 to elevate the tank 50v again above tank 49 and also to Shift the clutch-sleeve 42 to its middle position and stop the drum.

The liquid then Hows gradually from the tank 50 to the tank 49 until the latter is filled to such an extent that its weight will rotate the large wheel 48 still further in the same direction it moved last, thus shifting the clutch-sleeve 42 into engagement with the pulley 41 and rotating the nut 57 to separate its lug 60 from the lug 62 of t-he collar 55. The drum will now commence to operate in the original direction. Fig. 6 shows'the apparatus just at the moment when the clutch has been thus shifted.

It will be seen that the length of travel of the nut 57 between the two collars 55 and 56 will determine the extent' of rotation of the drum and the amount of travel of the cable in each direction. Also, by

This operation' causes the clutch-sleeve 42 to be thrownv over,

adjustin the valve 52 in the pipe 5l the rate of ow of liquid from one Itank to the other may be controlled and thereby the time between operations of the cable may be determined Within certain limits.

To prevent loss of heat, suitable curtain doors 64 may be hung at the front and rear ends of the furnace.

At'the discharge end of the furnace suitable hoppers-65 may be provided to receive the discharged material. These hoppers may discharge into the trough of a suitable conveyor 66, which may discharge the materials at one side of the furnace, from whence it may be removed in any suitableway.

The rotary gates 13 which supply the mix tothe charging conveyors lOfand 10b may be operated in any suitable way. As shown in the drawings, the shafts on which the rotary gates are mountedare rovided with sprocket Vwheels 67, each of w ich is driven by a chain 68 intermittently, by a `suitable source of power, not shown.

While, in the description hereinbefore, an'

alkali metal carbonate such as potassium orl sodium carbonate has been mentioned as particularly suitable in preparing the mix, it will be understood by those skilled in the art that any other compound of an alkaliforming metal such as an hydroxide of a suitable alkali metal may be employed as an equivalent for the alkali metal carbonate. The term alkali metal carbonate as used in the claims is therefore to Vbe construed as including the `use of such an equivalent.

What is claimed is:

1. The process of making chromates which consists 1n roasting, in an oxidizing atmosphere, a mix comprising a chrome ore, an alkali metal carbonate, and a relatively infusible alkaline absorbent, ata tem erature abovethe fusing point of the alk metal carbonate, submlttmg the material thus ob tained to successively lower temperatures until it has cooled below the fusion point of the alkali metal chromate formed, and during this cooling agitating the material until a granular product is obtained.

2. The process of making chromates which consists in gradually heating up a mix comprising a chrome ore, an alkali metal carbonate, and a relatively infusible alkaline absorbent to a temperature above the fusing point o f the alkali. metal carbonate, and then gradually cooling down the material to a temperature below the fusing point of the alkali metal chromate formed, agitatin the materials during the heating up an cooling down, and maintaining an oxidizing atmos here during the heating upA and cooling own until a granular product is obtained.

8. The process of making. chromates, which consists in maintaining a heated zone `having difering temperatures at diferent points in the length of thelzone, the maxi-v mum temperature being above the fusing point of fthe alkali metal carbonate and the minimum temperature being rbelow the fusing point of the alkali metal chromate formed, traveling a mix comprising a chrome ore, an alkali metal carbonate and a relatively infusible alkaline absorbent through such zone in such'a direction that the material, after passing through the maximum temperature, will subsequently pass to the minimum temperature, maintaining an oxidizin atmosphere in said zone, and continuous y agitatin the material while passing throng the eated zone until it has cooledbelow the fusing point of the alkali chromate formed until a granular product is obtained.

In testimony whereof, I have hereunto set my hand.

GEORGE P. FULLER. 

